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    <title>Three.js - Voxel Geometry - Textures</title>
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        margin: 0;
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        height: 100%;
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    <canvas id="c"></canvas>
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<script type="importmap">
{
  "imports": {
    "three": "../../build/three.module.js",
    "three/addons/": "../../examples/jsm/"
  }
}
</script>

<script type="module">
import * as THREE from 'three';
import { OrbitControls } from 'three/addons/controls/OrbitControls.js';

class VoxelWorld {

	constructor( options ) {

		this.cellSize = options.cellSize;
		this.tileSize = options.tileSize;
		this.tileTextureWidth = options.tileTextureWidth;
		this.tileTextureHeight = options.tileTextureHeight;
		const { cellSize } = this;
		this.cellSliceSize = cellSize * cellSize;
		this.cell = new Uint8Array( cellSize * cellSize * cellSize );

	}
	computeVoxelOffset( x, y, z ) {

		const { cellSize, cellSliceSize } = this;
		const voxelX = THREE.MathUtils.euclideanModulo( x, cellSize ) | 0;
		const voxelY = THREE.MathUtils.euclideanModulo( y, cellSize ) | 0;
		const voxelZ = THREE.MathUtils.euclideanModulo( z, cellSize ) | 0;
		return voxelY * cellSliceSize +
           voxelZ * cellSize +
           voxelX;

	}
	getCellForVoxel( x, y, z ) {

		const { cellSize } = this;
		const cellX = Math.floor( x / cellSize );
		const cellY = Math.floor( y / cellSize );
		const cellZ = Math.floor( z / cellSize );
		if ( cellX !== 0 || cellY !== 0 || cellZ !== 0 ) {

			return null;

		}

		return this.cell;

	}
	setVoxel( x, y, z, v ) {

		const cell = this.getCellForVoxel( x, y, z );
		if ( ! cell ) {

			return; // TODO: add a new cell?

		}

		const voxelOffset = this.computeVoxelOffset( x, y, z );
		cell[ voxelOffset ] = v;

	}
	getVoxel( x, y, z ) {

		const cell = this.getCellForVoxel( x, y, z );
		if ( ! cell ) {

			return 0;

		}

		const voxelOffset = this.computeVoxelOffset( x, y, z );
		return cell[ voxelOffset ];

	}
	generateGeometryDataForCell( cellX, cellY, cellZ ) {

		const { cellSize, tileSize, tileTextureWidth, tileTextureHeight } = this;
		const positions = [];
		const normals = [];
		const uvs = [];
		const indices = [];
		const startX = cellX * cellSize;
		const startY = cellY * cellSize;
		const startZ = cellZ * cellSize;

		for ( let y = 0; y < cellSize; ++ y ) {

			const voxelY = startY + y;
			for ( let z = 0; z < cellSize; ++ z ) {

				const voxelZ = startZ + z;
				for ( let x = 0; x < cellSize; ++ x ) {

					const voxelX = startX + x;
					const voxel = this.getVoxel( voxelX, voxelY, voxelZ );
					if ( voxel ) {

						// voxel 0 is sky (empty) so for UVs we start at 0
						const uvVoxel = voxel - 1;
						// There is a voxel here but do we need faces for it?
						for ( const { dir, corners, uvRow } of VoxelWorld.faces ) {

							const neighbor = this.getVoxel(
								voxelX + dir[ 0 ],
								voxelY + dir[ 1 ],
								voxelZ + dir[ 2 ] );
							if ( ! neighbor ) {

								// this voxel has no neighbor in this direction so we need a face.
								const ndx = positions.length / 3;
								for ( const { pos, uv } of corners ) {

									positions.push( pos[ 0 ] + x, pos[ 1 ] + y, pos[ 2 ] + z );
									normals.push( ...dir );
									uvs.push(
										( uvVoxel + uv[ 0 ] ) * tileSize / tileTextureWidth,
										1 - ( uvRow + 1 - uv[ 1 ] ) * tileSize / tileTextureHeight );

								}

								indices.push(
									ndx, ndx + 1, ndx + 2,
									ndx + 2, ndx + 1, ndx + 3,
								);

							}

						}

					}

				}

			}

		}

		return {
			positions,
			normals,
			uvs,
			indices,
		};

	}

}

VoxelWorld.faces = [
	{ // left
		uvRow: 0,
		dir: [ - 1, 0, 0, ],
		corners: [
			{ pos: [ 0, 1, 0 ], uv: [ 0, 1 ], },
			{ pos: [ 0, 0, 0 ], uv: [ 0, 0 ], },
			{ pos: [ 0, 1, 1 ], uv: [ 1, 1 ], },
			{ pos: [ 0, 0, 1 ], uv: [ 1, 0 ], },
		],
	},
	{ // right
		uvRow: 0,
		dir: [ 1, 0, 0, ],
		corners: [
			{ pos: [ 1, 1, 1 ], uv: [ 0, 1 ], },
			{ pos: [ 1, 0, 1 ], uv: [ 0, 0 ], },
			{ pos: [ 1, 1, 0 ], uv: [ 1, 1 ], },
			{ pos: [ 1, 0, 0 ], uv: [ 1, 0 ], },
		],
	},
	{ // bottom
		uvRow: 1,
		dir: [ 0, - 1, 0, ],
		corners: [
			{ pos: [ 1, 0, 1 ], uv: [ 1, 0 ], },
			{ pos: [ 0, 0, 1 ], uv: [ 0, 0 ], },
			{ pos: [ 1, 0, 0 ], uv: [ 1, 1 ], },
			{ pos: [ 0, 0, 0 ], uv: [ 0, 1 ], },
		],
	},
	{ // top
		uvRow: 2,
		dir: [ 0, 1, 0, ],
		corners: [
			{ pos: [ 0, 1, 1 ], uv: [ 1, 1 ], },
			{ pos: [ 1, 1, 1 ], uv: [ 0, 1 ], },
			{ pos: [ 0, 1, 0 ], uv: [ 1, 0 ], },
			{ pos: [ 1, 1, 0 ], uv: [ 0, 0 ], },
		],
	},
	{ // back
		uvRow: 0,
		dir: [ 0, 0, - 1, ],
		corners: [
			{ pos: [ 1, 0, 0 ], uv: [ 0, 0 ], },
			{ pos: [ 0, 0, 0 ], uv: [ 1, 0 ], },
			{ pos: [ 1, 1, 0 ], uv: [ 0, 1 ], },
			{ pos: [ 0, 1, 0 ], uv: [ 1, 1 ], },
		],
	},
	{ // front
		uvRow: 0,
		dir: [ 0, 0, 1, ],
		corners: [
			{ pos: [ 0, 0, 1 ], uv: [ 0, 0 ], },
			{ pos: [ 1, 0, 1 ], uv: [ 1, 0 ], },
			{ pos: [ 0, 1, 1 ], uv: [ 0, 1 ], },
			{ pos: [ 1, 1, 1 ], uv: [ 1, 1 ], },
		],
	},
];

function main() {

	const canvas = document.querySelector( '#c' );
	const renderer = new THREE.WebGLRenderer( { antialias: true, canvas } );

	const cellSize = 32;

	const fov = 75;
	const aspect = 2; // the canvas default
	const near = 0.1;
	const far = 1000;
	const camera = new THREE.PerspectiveCamera( fov, aspect, near, far );
	camera.position.set( - cellSize * .3, cellSize * .8, - cellSize * .3 );

	const controls = new OrbitControls( camera, canvas );
	controls.target.set( cellSize / 2, cellSize / 3, cellSize / 2 );
	controls.update();

	const scene = new THREE.Scene();
	scene.background = new THREE.Color( 'lightblue' );

	function addLight( x, y, z ) {

		const color = 0xFFFFFF;
		const intensity = 3;
		const light = new THREE.DirectionalLight( color, intensity );
		light.position.set( x, y, z );
		scene.add( light );

	}

	addLight( - 1, 2, 4 );
	addLight( 1, - 1, - 2 );

	const loader = new THREE.TextureLoader();
	const texture = loader.load( 'resources/images/minecraft/flourish-cc-by-nc-sa.png', render );
	texture.magFilter = THREE.NearestFilter;
	texture.minFilter = THREE.NearestFilter;
	texture.colorSpace = THREE.SRGBColorSpace;

	const tileSize = 16;
	const tileTextureWidth = 256;
	const tileTextureHeight = 64;
	const world = new VoxelWorld( {
		cellSize,
		tileSize,
		tileTextureWidth,
		tileTextureHeight,
	} );

	for ( let y = 0; y < cellSize; ++ y ) {

		for ( let z = 0; z < cellSize; ++ z ) {

			for ( let x = 0; x < cellSize; ++ x ) {

				const height = ( Math.sin( x / cellSize * Math.PI * 2 ) + Math.sin( z / cellSize * Math.PI * 3 ) ) * ( cellSize / 6 ) + ( cellSize / 2 );
				if ( y < height ) {

					world.setVoxel( x, y, z, randInt( 1, 17 ) );

				}

			}

		}

	}

	function randInt( min, max ) {

		return Math.floor( Math.random() * ( max - min ) + min );

	}

	const { positions, normals, uvs, indices } = world.generateGeometryDataForCell( 0, 0, 0 );
	const geometry = new THREE.BufferGeometry();
	const material = new THREE.MeshLambertMaterial( {
		map: texture,
		side: THREE.DoubleSide,
		alphaTest: 0.1,
		transparent: true,
	} );

	const positionNumComponents = 3;
	const normalNumComponents = 3;
	const uvNumComponents = 2;
	geometry.setAttribute(
		'position',
		new THREE.BufferAttribute( new Float32Array( positions ), positionNumComponents ) );
	geometry.setAttribute(
		'normal',
		new THREE.BufferAttribute( new Float32Array( normals ), normalNumComponents ) );
	geometry.setAttribute(
		'uv',
		new THREE.BufferAttribute( new Float32Array( uvs ), uvNumComponents ) );
	geometry.setIndex( indices );
	const mesh = new THREE.Mesh( geometry, material );
	scene.add( mesh );

	function resizeRendererToDisplaySize( renderer ) {

		const canvas = renderer.domElement;
		const width = canvas.clientWidth;
		const height = canvas.clientHeight;
		const needResize = canvas.width !== width || canvas.height !== height;
		if ( needResize ) {

			renderer.setSize( width, height, false );

		}

		return needResize;

	}

	let renderRequested = false;

	function render() {

		renderRequested = undefined;

		if ( resizeRendererToDisplaySize( renderer ) ) {

			const canvas = renderer.domElement;
			camera.aspect = canvas.clientWidth / canvas.clientHeight;
			camera.updateProjectionMatrix();

		}

		controls.update();
		renderer.render( scene, camera );

	}

	render();

	function requestRenderIfNotRequested() {

		if ( ! renderRequested ) {

			renderRequested = true;
			requestAnimationFrame( render );

		}

	}

	controls.addEventListener( 'change', requestRenderIfNotRequested );
	window.addEventListener( 'resize', requestRenderIfNotRequested );

}

main();
</script>
</html>
